It is known that individual nuclear particles are so constituted as to permit fusing of the lighter nuclei. Fusion of lighter nuclei is accompanied by release of energy. Of particular interest, is any fusion reaction in which power can be produced in quantities greater than the power consumed in establishing and maintaining the reaction. There are over thirty reactions now known to be possible. The most appealing reactions are those which involve the heavy hydrogen isotopes, deuterium and tritium, because they tend to have the largest fusion reaction cross section at the lowest energies. Many possible reactions are well known. For example, Van Norstrand's Scientific Encyclopedia, Fifth Edition, Reinhold Company, New York, N.Y., 1976, at page 1656, et seq., discusses various aspects of the possibilities for producing a net gain in power from fusion reactions and briefly describes some of the attempts to perform such reactions with a net power gain.
Plasma research has received concentrated attention, but the formidable task of plasma containment has yet to be solved. In avoidance of the problems of containment, a more recent approach involves laser-induced fusion. In its simplest form a focused energetic laser beam is brought to bear on a small deuterium-tritium pellet for heating to fusion temperatures. Efforts on this and on other fronts such as those involving containment have been steady in response to high incentives.
Thus, while many of the possibilities have long been known and have been widely attacked through various approaches towards achieving net power gain from fusion, the challenge remains unsatisfied.
A central problem of deuterium fusion for power production is that of raising a small mass of ionized deuterium or a mixture of deuterium and tritium to the necessary reaction temperature while maintaining the density of the plasma and temperature long enough for a sufficient portion of the hot ionized gas to proceed with a nuclear reaction. The necessary temperature required is of the order of 10.sup.8 K.degree., such that no solid state matter can maintain mechanical integrity while in close contact with the reaction. It is therefore necessary to either confine the reacting plasma with a magnetic field or to pulse the reaction so rapidly that inertial forces from rapidly moving high temperature gases can be used to provide the confinement forces for the short time necessary.
Magnetic confinement of the reacting plasma has been attempted in many forms. Such previously developed forms have suffered from instabilities which have allowed the hot plasma to leak through the confining fields too rapidly. A deficiency in prior systems is the amount of thermodynamic equilibrium time required because heat is frequently introduced by heating the electrons of the plasma. If the plasma is thin, the thermodynamic equilibrium time necessary for the positive ionic temperature to equal the electron temperature where the reaction can occur is too long compared to the stability time. The particle leak rate of the magnetic confinement system must also permit a confinement time longer than the instability or the electron-ion thermodynamic equilibrium time.
Several factors of a magnetic confinement system are important for allowing the required reaction time and plasma density to be reached. These factors include the field strength and gradient of the magnetic field, the particle density and density gradient of the plasma and the stability time of the plasma confinement. All these factors interact and influence the confinement time.
A need has thus developed for a fusion reactor which greatly extends confinement time and increases the effectiveness of the other factors involved in nuclear fusion utilizing a confinement system which will provide long confinement time. Such a natural system is the Van Allen belts of radiation around the earth. In these belts an ion plasma of sufficient temperature to sustain deuterium-deuterium fusion is confined by a small magnetic field with a relaxation time of many months. The Van Allen belts of radiation are created by charged particles reflected in a north-south oscillation by "magnetic mirrors" formed by the increasing intensity of the magnetic fields in the higher latitudes of the earth. This natural system of magnetic mirrors makes use of fields on the outside of the earth's "magnet".
A need has thus arisen for a fusion reactor utilizing a magnetic confinement system of magnetic mirrors with the "natural" geometry reproduced on a realizable scale to increase plasma density without a detrimental reduction in stability time. A need has further arisen for such a magnetic system in which provision is made for an input of heating energy to raise the temperature of the plasma to the required reaction temperature.